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TROPICAL DEPRESSION OLGA DISCUSSION NUMBER  39
NATIONAL WEATHER SERVICE MIAMI FL
4 AM EST TUE DEC 04 2001
 
OLGA REMAINS A VERY PERSISTENT AND WELL DEVELOPED CIRCULATION. 
SATELLITE IMAGERY INDICATES THAT SIGNIFICANT CONVECTION...TOPS TO 
-60C...HAS ONE AGAIN DEVELOPED JUST EAST OF THE LOW-LEVEL CENTER. 
DVORAK SATELLITE INTENSITY ESTIMATES FROM ALL THREE AGENCIES IS 
30 KT...T2.0...WITH SHEAR PATTERN DATA T-NUMBERS NEAR T2.5...OR 
35 KT.  OUTFLOW IS RESTRICTED TO THE EASTERN SEMICIRCLE OWING TO THE 
MODERATE UPPER-LEVEL SOUTHWESTERLY SHEAR IMPINGING ON THE CYCLONE.

THE INITIAL MOTION ESTIMATE IS 090/06.  HOWEVER...A DECREASE IN 
FORWARD SPEED AND A TURN TO THE SOUTH OR SOUTHWEST IS EXPECTED TO 
DEVELOP LATER TODAY OR TONIGHT. WATER VAPOR IMAGERY INDICATES THE 
DEEP-LAYER TROUGH TO THE NORTH IS MOVING RAPIDLY AWAY FROM OLGA 
WHILE A BROAD UPPER-LEVEL TROUGH IS DIGGING SOUTHWARD ALONG THE WEST 
SIDE OF THE CYCLONE.  IT ALSO APPEARS THAT A SMALL VORTICITY CENTER 
MAY BE TRACKING INWARD TOWARD THE CENTER OF OLGA AND THIS COULD ADD 
A LITTLE MORE ENERGY TO THE SYSTEM AND MAKE THE VERTICAL CIRCULATION 
A LITTLE STRONGER AND DEEPER...AND MORE SHEAR RESISTANT.  THE NHC 
MODEL GUIDANCE IS LESS DIVERGENT THAN THIS TIME YESTERDAY AND THE 
FORECAST TRACKS ARE CONFINED TO THE SOUTHERN SEMICIRCLE IN RESPONSE 
TO THE DEEP-LAYER RIDGE BUILDING BACK IN TO THE NORTH OF OLGA.  ALL 
OF THE GLOBAL MODELS AND THE 3 BAM MODELS TAKE OLGA SOUTH AND THEN 
SOUTHWESTWARD DURING THE NEXT 24 HOURS...WITH A GRADUAL TURN TO THE 
WEST-SOUTHWEST OR WEST IN 36 TO 48 HOURS. ALL OF THE GLOBAL MODELS 
ALSO AGREE ON THE REMNANT CIRCULATION OR INVERTED TROUGH PASSING 
ACROSS THE CENTRAL AND NORTHERN BAHAMAS AND SOUTH FLORIDA IN 72 TO 
96 HOURS. GIVEN THE TENACITY OF THIS SYSTEM...AND THE FACT THAT IT 
IS FORECAST TO TRACK OVER WARMER WATER...I HAVE DECIDED TO ADD A 
72-HOUR POSITION FOR CONTINUITY PURPOSES IN THE EVENT OLGA DECIDES 
TO RE-STRENGTHEN BACK TO A SIGNIFICANT TROPICAL CYCLONE.  
 
GIVEN THE SOMEWHAT HYBRID NATURE OF THIS SYSTEM...IT IS DIFFICULT TO 
ASSESS WHAT EFFECT VERTICAL SHEAR WILL HAVE ON OLGA DURING THE NEXT 
24 HOURS.  BASED ON THE LATEST SATELLITE IMAGES...THE UPPER-LEVEL 
SHEAR APPEARS TO BE HAVING LITTLE EFFECT OTHER THAN TO DISPLACE THE 
CONVECTION TO THE EAST OF THE CENTER.  HOWEVER...ALL OF THE GLOBAL 
MODELS AGREE THAT THE SHEAR WILL LESSEN AND BECOME MORE NORTHERLY 
DURING THE NEXT 24 HOURS...WHICH WILL BE ALONG THE FORECAST TRACK.  
BY 36 HOURS...A 200 MB ANTICYCLONE IS FORECAST TO DEVELOP JUST NORTH 
OF OLGA...PLACING THE CYCLONE UNDER MORE FAVORABLE LIGHT UPPER-LEVEL 
EASTERLY FLOW.  GIVEN THAT OLGA WILL BE TRACKING SOUTHWARD OVER 
WARMER WATER...SSTS NEAR 26C... SIGNIFICANT RE-DEVELOPMENT IS A 
DISTINCT POSSIBILITY...ESPECIALLY IF A LOW-LEVEL CIRCULATION REMAINS 
INTACT AFTER 36 TO 48 HOURS.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     04/0900Z 27.8N  67.9W    30 KTS
12HR VT     04/1800Z 27.4N  67.6W    30 KTS
24HR VT     05/0600Z 26.3N  68.4W    25 KTS...DISSIPATING
36HR VT     05/1800Z 25.2N  70.0W    25 KTS...DISSIPATING
48HR VT     06/0600Z 24.5N  72.2W    20 KTS...REMNANT LOW
72HR VT     07/0600Z 24.5N  78.0W    20 KTS...REMNANT LOW
 
 
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